1. Field of the Invention
The invention relates in general to a method and an apparatus for controlling a TX power amplifier, and more particularly to a method and an apparatus for controlling a TX power amplifier applied in a wireless communication system.
2. Description of the Related Art
A wireless communication system is used for transmitting data through the air to a remote end. The TX power amplifier (TX PA) amplifies the power of signals in order to prevent signals from being weakened to be indistinguishable noise before the signals reach the target remote end. Generally speaking, the power of the TX PA for signal transmission is increased to a predetermined amplitude before the signal transmission. The process of power increment occurs in a ramp-up division. After the signal transmission, the power of the TX PA for signal transmission is decreased to a minimum amplitude. The process of power decrement occurs in a ramp-down division.
The Time Division Multiple Access (TDMA) system takes one time slot as a unit for transmitting/receiving data. Any two cellular phones will not transmit data in the same time slot (namely, the same time, the same frequency) so as to avoid interferences. Further, the rear portion of a time slot and the front portion of a subsequent times lot are defined as a guard area, and no data transmission occurs in the guard area so as to avoid interferences. Moreover, data for multiple time slots can be continuously transmitted in the TDMA system, and the transmission power for each of the time slots may be varied. When the TDMA system continuously transmits data for multiple time slots, it has to perform the power transformation in the guard area between two continuous time slots. The process of power transformation occurs in an inter-ramp division.
No matter the power amplitudes for two continuous time slots S1 and S2 are progressively increasing, progressively decreasing, or constant, in the TDMA system, the power control curve, representing the power variation of the conventional TX power amplifier for signal transmission, is linear in the ramp-up division, ramp-down division, and inter-ramp division.
Referring to FIGS. 1A to 1C, the timing charts show the variation of power amplitude of a conventional TX power amplifier for signal transmission when continuously transmitting data for two time slots in the TDMA system. As shown in FIG. 1A, the power amplitudes for two continuous time slots S1 and S2 are progressively increased. The inter-ramp control curve IRa is a linear increasing line, and the power amplitudes in the inter-ramp division are greater than the power amplitude of the time slot S1 and less than the power amplitude of the time slot S2. As shown in FIG. 1B, the power amplitudes for two continuous time slots S1 and S2 are progressively decreased. The inter-ramp control curve IRb is a linear decreasing line, and the power amplitudes in the inter-ramp division are less than the power amplitude of the time slot S1 and greater than the power amplitude of the time slot S2. As shown in FIG. 1C, the power amplitudes for two continuous time slots S1 and S2 are constant. The inter-ramp control curve IRc is a horizontal line, and the power amplitudes in the inter-ramp division are the same as the power amplitudes of the time slot S1 and S2. Furthermore, the ramp-up control curve RUa, RUb and RUc are linear increasing lines while the ramp-down control curve RDa, RDb and RDc are linear decreasing lines.
Conventionally, for the ramp-up and ramp-down divisions, the TDMA system has to store the ramp-up control curves and ramp-down control curves corresponding to various power amplitudes in the memory, requiring a large memory space, and applies linear operations for generating inter-ramp control curves for the TX PA. Because the ramp-up control curves and ramp-down control curves are stored in the memory, the conventional approach is able to rapidly generate a power control curve by accessing the memory, but it takes large memory to store a large amount of ramp-up control curves and ramp-down control curves. For the inter-ramp division, because there are many possible combinations of power amplitudes for two continuous time slots, there are too many inter-ramp control curves to store in the memory. Furthermore, in consideration of the operational complexity, the conventional approach generates the inter-ramp control curves for the TX PA by applying simple linear operations.
However, a very large proportion of the power consumption for the whole system is generally resulted from the power consumption of the TX PA. In particular, the larger the signal transmission power is, the larger the power consumption is. In the design of linear connection of two continuous time slots, even though the TX PA does not transmit any data in the inter-ramp division, it still consumes a lot of power.